Extraction of the Periodic Components of Solar Activity with the EMD Method

The EMD (empirical mode decomposition) method has exhibited superiority and potential in applications related to the processing of nonlinear and unsteady time sequences. For the research of periodicity of solar activity by means of the EMD method, the monthly mean values of sunspot numbers in 110 years (1894–2003) and 55 years (1949-2003) are analyzed, resulting in a series of modes and one trend term. For all of them the periodic components of 1.3–1.4 years, QBO (quasi-biannual oscillation) components of 25–30 months, the 11-year solar cycle component as well as the 22-year Hale cycle component are possibly included. The amplitude of the component of the 11-year cycle is the largest, and the characteristics of variation of this component are highly correlated with the original data of sunspot numbers. Being different from traditional methods, the EMD technique can provide the characteristics of isolated features on various time scales.